Loudspeaker



' c. R. MINER Dec. 17, 1963 LOUDSPEAKER Filed Jan. 16, 1961 FIG. 3.

INVENTOR. CARROLL R.MINER ATTORNEY.

United States Patent Ofi ice 7, su tes Patented Dec. l7, 1963 3,114,429 LQUDSPEAKER Carroll R. Miner, Whittier, lCalih, assignor to Hoffman Electronics Corporation, acorporation of California Filed Jan. 16, 195i. Ser. No. 82,8ll2 11 Claims. (tCl. l$131) The present invention relates to electric-acoustic trans- At low frequencies, however, there is great diiliculty in securing adequate coupling between the moving diaphragm and the air to develop sound pressures that are comparable to the efficiency of the speaker at higher frequencies. This is because of several factors, such as the compressibility of the air and the fact that low frequency energy values in music are quite large and, therefore, require greater movement of air than do higher frequencies.

conventionally, devices such as bass-reflex enclosures and infinite baffles have been used'to improve the ability of a given size cone loudspeaker to move large amounts of air and thereby develop the required sound pressure for the cone to be acceptable. These devices, however, are not without their own defects which prevent them from being realistic and natural in the quality of the sound they create. This is because enclosures of that kind are acoustically resonant, and, while they assist in increasing a means of superior low frequency sound reproduction without relying upon acoustic devices such as cabinets, boxes, or horns.

According to the present invention, a loudspeaker device comprises a conventional dynamic loudspeaker with a conventional paper cone, but having an additional diaphragm that is made of a material such as Styrofoam, which has a hi h stitlness-to-mass ratio, so as to increase the effective area of the radiating surface without seriously increasing the over-all front-to-rear depth of the loudspeaker.

The features of the present invention which are believed to be novel are set forth with particularity in the'appended claims. The present invention, both as to its organization and manner of operation, together with further ob jects and advantages thereof, may best be understood by reference to the following description, taken in connecsound pressure, they accomplish this at essentially one frequency, which causes an unnatural and sometimes annoying sound. In addition, enclosures of this kind, to be efficient, must be quite large and do not lend themselves to use in conventionally-sized rooms in the average home. Small enclosure and speaker combinations have been developed recently, but they are low in efiiciency and suffer more seriously from the resonant character of sound previously referred to.

Another method of achieving the required movement of air at low frequencies is through the use of large cones or diaphragms, which are coupled directly to a large volume of air without the use of acoustic enclosures or other coupling devices. This may be done by using a single large diaphragm or by the use of a number of smaller diaphragms, the total area of all of them achieving the desired coupling with the air. However, when the diaphragm size of a loudspeaker is increased, its performance at higher frequencies is generaly impaired, because of the inability of the greater mass of the material constituting the diaphragm to move in response to high frequency signals. it is because of this problem that multiple arrays of different-size speakers are frequently used. Electrical dividing networks are used to separate the signal into ranges of frequencies which are suitable for each loudspeaker. The low frequency speaker, which is the largest one, is referred to as a woofer-f and only low frequencies are fed to it, while mid-range and high-frequency speakers of smaller size are used for the higher frequen cies of the upper range of sound.

It is an object of the present invention, therefore, to provide a novel loudspeaker.

It is a further object of the present invention to provide a wide-range loudspeaker having superior low frequency performance without impairment of its operation at higher frequencies.

It is another object of the present invention to provide tion with the accompanying drawings, in which:

FEGURE l is a sectional view of a loudspeaker according to the present invention. i 7

FIGURE 2 'is a sectional view or" another embodiment of the present invention.

FIGURE 3 is an isometric view showing a plurality of loudspeakers, each according to the embodiment shown in FIGURE 2, mounted as a unit.

FIGURE 4 is a sectional view taken along line 44 of FIGURE 3. p

, Referring now to the drawings, FIGURE 1 shows loudspeaker ljl having permanent magnet 12, base plate 13, and soft-iron pole piece l4. Cover plate 15 is attached to the other end of magnet 12 to provide an annular air in which there is a uniform radial magnetic flux density. Voice coil Zil is a solenoid of copper wire wound on cylindrical form 21, which is centered in the air gap by flexible spider 2. Dome-shaped dust cover 23 prevents air leakage. Paper cone 24 is rigidly connected to form 21. Base 25 of cone 24 is stiffened by corrugations 26 and is fastened to metal supports 27 and cabinet 28.

Panel 31 is a diaphragm made of a material such as polystyrenefoam or Styrofoam having a high stiffness-to.- mass ratio. Panel 31 is cemented to paper collar 32, which in turn is cemented to ring 33 of compliant material such as Polyurethane foam. Compliant ring 33 is in turn cemented to paper cone 24; The function of compliant ring 33 is to isolate panel 31 from cone 24 at middie and high frequencies, thereby permitting normal operation of cone 234 at those frequencies. Compliant ring 33 may be eliminated if wide-range operationis not desired, in which case the loudspeaker may be used as a woofer. Panel Si is planar, rectangular, about /2 inch thick, and contains opening 34.

The voice coil assembly is free to move along its axis and to carry with it cone 2d and panel 31, which move and thereby radiate sound, as a result of the axial forces generated in the voice coil by interaction of the signal current and the steady radial magnetic field. Cone 24 drivcs'panel 31 and produces a relatively high amplitude sound wave at very low frequencies.

Panel 31 must have a high stiflness-to-mass ratio so that it will be sufficiently rigid to be vibrated without flexing and yet sufliciently light so'that it can be vibrated easily. Panel 31 would not operate properly if made out of paper, since paper does not have a sufficiently high stifiness-to-mass ratio. Panel 31 increases the effective area of cone 24, making a small speaker effectively a large speaker with little increase in physical depth. Panel radiating area of a six-inch speaker is approximately 20 3 square inches, which would be increased to 100 square inches by the addition of the -inch Styrofoam panel.

FIGURE 2 shows a modified version of the panel. Panel 36 is formed into a dish to assist in making it rigid and also to eliminate the need for collar 32 used in FIG- URE 1. Lip 37 is provided for added stiffness. The compliant ring still may or may not be used, depending upon the range of frequencies it is desired to cover. Molded panel 36 is thinner than panel 31, since adequate stiffness is achieved by the dish-like shape. This is desirable since less material is used, which fact further reduces the mass of the panel.

FIGURE 3 shows. panels 41, 42, and 43, each being identical to panel 36 and made in accordance with the present invention. Panels 41 and 42 are resiliently con nected together byfiexible bellows 44, as is shown more clearly in FIGURE 4. Panels 42 and 43 are resiliently connected together by flexible bellows 45, which is similar to bellows 44. The panels are connected together in this manner to prevent leakage of air pressure between them, which would otherwise reduce their effectiveness at low frequencies. If desired, panels 41, 42, and 43 could be made of one large piece of Styrofoam. It is preferable, however, that the panels be separated as shown, in order to avoid the mechanical strains that would result from shrinkage of the Styrofoam panel with age.

A flexible connection is provided between the Styrofoam panels and mounting frame 51 by means of felt layer 52. The purpose of cementing felt layer 52 between the panels and frame 51 is to prevent air leakage around the ends of the panels, which would reduce their effectiveness in developing sound pressure at low frequencies.

While particular embodiments of the present invention have been shown and described, it will be obvious to those skilled in the art that changes and modifications may be made without departing from this invention in its broader aspects, and, therefore, the aim in the appended claims is to cover all such changes and modifications as fall within the true spirit and scope of this invention.

I claim:

1; A loudspeaker device comprising: a loudspeaker having a vibratory cone connected at its base end to a rigid support member; a rectangular planar panel having a central opening and a high stiffness-to-mass ratio; and a cylindrical'co'llar, said panel being connected by means of said collar to the base region of said cone for vibration therewith, said opening being of substantially the same diametc-r as said base region, and said panel being-mounted 4 so that said opening is co-axial with respect to said base region.

2. Apparatus as defined in claim 1 in which said panel is made of Styrofoam.

3. A loudspeaker device comprising: a loudspeaker having a vibratory cone connected at its base end to a rigid support member; and a rigid diaphragm connected to the base region of said cone for vibration therewith, said diaphragm having a central opening therein that is of substantially the same diameter as said base region, and said diaphragm being mounted so that said opening is co-axial with respect to said base region.

4. Apparatus as defined in claim 3 in which said diaphragm is rectangular in shape.

5. Apparatus as defined in claim 4 in which said diaphragm is made of Styrofoam.

6. Apparatus as defined in claim 5 in which said diaphragm is connected to said base by means of a compliant material.

7. Apparatus as defined in claim 6 in which said compliant material is Polyurethane foam.

8. Apparatus as defined in claim 7 in which said diaphragm is a planar panel.

9. A loudspeaker device comprising: a loudspeaker having a vibratory cone connected at its base end to a rigid support member, and a rigid diaphragm mounted coaxially with respect to said cone and connected to the base region thereof for vibration therewith.

10. A loudspeaker device comprising: a loudspeaker having a vibratory cone connected at its base end to a rigid support member, and :a rigid diaphragm mounted co axially with respect to said cone and connected thereto for vibration therewith.

11. Apparatus as defined in claim 10 in which said diaphragm is rectangular in shape.

References Cited in the file of this patent UNITED STATES PATENTS 1,763,054 Hopkins June 10, 1930 2,439,666 Marquis Apr. 13, 1948 2,630,189 Julie Mar. 3, 1953 2,685,935 Lenz Aug. 10, 1954 2,853,146 Coates Sept. 23, 1958 2,926,741 Rohn et al. Mar. 1, 1960 FOREIGN PATENTS 265,908 Great Britain July 13, 1927 

1. A LOUDSPEAKER DEVICE COMPRISING: A LOUDSPEAKER HAVING A VIBRATORY CONE CONNECTED AT ITS BASE END TO A RIGID SUPPORT MEMBER; A RECTANGULAR PLANAR PANEL HAVING A CENTRAL OPENING AND A HIGH STIFFNESS-TO-MASS RATIO; AND A CYLINDRICAL COLLAR, SAID PANEL BEING CONNECTED BY MEANS OF SAID COLLAR TO THE BASE REGION OF SAID CONE FOR VIBRATION THEREWITH, SAID OPENING BEING OF SUBSTANTIALLY THE SAME DIAMETER AS SAID BASE REGION, AND SAID PANEL BEING MOUNTED SO THAT SAID OPENING IS CO-AXIAL WITH RESPECT TO SAID BASE REGION. 